Ketone polysulfides



acsasss KETONE fOLYSULFlDES Lawrence E. Forman, Akron, Ohio, assignor to The Firestone Tire 8: Rubber Company, Akron, Ohio, a corporation of Ohio N Drawing. Filed Apr. 14, 1058, Ser. No. 728,032

9 Claims. (Ql. 260-63) This invention relates to curing agents for sulfur-vu1- caniza'ble rubber-like materials and, more particularly, to improved polysulfide type curing agents and curing processes in which these improved curing agents are employed.

In preparing a rubber composition for vulcanization or curing, the raw rubber (natural, synthetic or mixtures of natural and synthetic rubbers) is mixed with various compounding agents, including a curing agent and optionally one or more of the following: a softener or plasticizer, stearic acid or other pigment dispersing agent, carbon black, zinc oxide, silica, a carbonate filler or other filler, an accelerator, an activator or retarder, an antioxidant, and reclaimed rubber or a rubber extender. These components can be worked into a homogeneous composition in a banbury or on mixing rolls which are cooled to a temperature of about 70 C. to dissipate the frictional heat generated in the compounding operation. However, the rubber composition itself often reaches a temperature as high as 100-110 0., depending upon operating conditions. Consequently, the primary vulcanizing agent and any accelerators or activators employed therewith should not effect a substantial pie-vulcanization or scorching during the compounding operation as a result of the temperatures obtained. Alternatively, the rubber can be compounded in latex or water dispersion, as is known in the art.

As the art of vulcanizing rubber polymers has progressed, agents effecting a more rapid curing, either in conjunction with elemental sulfur or by themselves, have been developed for use in manufacturing rubber products. It has long been known that various organic compounds, including certain mercaptans, organic sultides, substituted guanidines and aldehyde-amine condensates, greatly accelerate the vulcanizing action of elemental sulfur. Similarly, such compounds as the tetramethylthiuram monoand di-sulfides, the metal dithiocarbamates, and various amines and amine salts have been found effective as secondary accelerators or activators. Many of these commonly employed materials, however, have been found undesirable, inter alia, because of their tendencies to promote scorching during the milling, extruding and calendering operations commonly employed in manufacturing rubber products.

More recently, it has been found possible to vulcanize or cure a sulfur-vulcanizable rubber by treating it with a phenol polysulfide in the absence of elemental sulfur, this process being known as NES curing. The phenol polysulfides having the probable structural formula:

l R n have been found effective, both in accelerating the vulcanizing action of elemental sulfur and as a primary vulcanizing agent in NES curing.

An object of this invention is to provide a new class of organic polysulfide curing agents characterized by their ability to cure sulfur-vulcanizable rubber compositions efficiently in the absence of free sulfur.

A further object of the invention is to provide a process rates atent ice for producing a new class of organic polysulfide curing agents which efficiently and economically may be employed in the curing of sulfur-vulcanizable rubbers.

An additional object of the invention is to provide a process for curing sulfur-vulcanizable rubbers containing a new class of polysulfide curing agents produced from enolizable ketones.

Generally described, the present invention comprises a polysulfide effective as a curing agent for sulfur-vulcanizable rubbers having the structural formula:

wherein A is hydrogen, alkyl, ketoalkyl, acyl, aryl, alkaryl or aralkyl; B is H, alkyl, ketoalkyl, acy aryl, alkaryl or aralkyl; wherein A and B can be joined in a ring; wherein 111 is l to 3 and n is at least 2', and wherein Z is H, X (a halogen).

l H-O \C- ii I A B l -G \O'B ll 1 A B Since the molecular weights of the resins are not necessarily critical, the value for n can vary over a wide range of from 2 to or even 1000.

The present invention further includes a process for producing a polysulfide curing agent for sulfur-vulcanizable rubbers, which comprises reacting with a polysulfur halide (a polysulfur chloride, bromide or iodide) an enolizable ketone which, in the enol form, has the structural formula:

ii I

wherein A is hydrogen, alkyl, ketoalkyl, acyl, aryl, alk aryl or aralkyl; B is H, alkyl, ketoalkyl, acyl, aryl, alkaryl or aralkyl; and wherein A and B can be joined in a ring.

Also embraced by the invention is a process for curing a sulfur-vulcanizable rubber which comprises admixing with the rubber a polysulfide having the structural Formula l and heating the mixture to a vulcanizing temperature to form a vulcanizate.

In accordance with the present invention, it has been discovered that polysulfide compounds, equally effective curing agents to polyphenol sulfides, can be prepared by reacting an enolizable ketone with a sulfur monohalide or higher sulfide of chlorine, bromine or iodine. Ketones which are enolizable normally exist in a state wherein a portion of the ketone is in the tautomeric enol configuration and is in equilibrium with the ketone present in the keto configuration. When such ketones are reacted with a sulfur chloride in accordance with the invention, the polysulfur chloride and enol tautomer form a polysulfide and hydrochloric acid. The insolubility of the hydrochloric acid in the reaction mixture and its elimination promotes the rapid conversion of xetones in the keto form to the enol tautomer. This process thus continues until substantially all of the ketone is converted to the enol form and is reacted with the sulfur chloride to form the polysulfide.

Alternasuch as monochloroand monofiuorobenzene, chloroform, trichloroethylene, tetrachloroethane, propylene dichloride and the like.

The polysulfides prepared in accordance with the presvulcanizable rubbers employed by the art including, without limitation, various synthetic rubbers such as SBR (butadiene-styrene), BR (butadiene rubbers),

isoprene rubbers), neoprene (polychloroprene or CR), butyl rubber (HR), and suitable mixtures thereof. (The abbreviations are in accord with the ASTM designation: D141856T.) The usual curing temperatures employed by the art can also be employed When using the polysulfides of the present invention. For best results, curing temperatures of from about 140 to about 400 F. and preferably from about 250 to about 350 F. are emare employed in the same concentrations as the phenol polysulfides and other curing agents currently employed in the art, for example, from one to fifty parts of curing agent per hundred parts of the rubber (phr.).

aving generally described the invention, the following les are presented to illustrate the production of the polysulfides of the invention and their utility as curing EXAMPLE 1 crystals are green, have a melting point of 119-120 and are identified as sulfur. The filtrate is heated to boiling, activated carbon is added, and the solution is filtered.

4 This procedure is repeated three times. The resulting liquid is steam distilled to remove volatile solvent.

(:0 CH3 n EXAMPLE 2 (1 mole) of acetone and ml. of benzene are placed in a 3-neck, l-liter, round-bottom flask equipped with a reflux condenser and a dropping funnel. The solution is heated to boiling, and then a solution of 35.2 grams 1.1 gram-atoms) of sulfur and 148.5 grams 1.1 moles) of sulfur monochloride in 75 ml. of benzene is added dropwise. The reaction mixture HCl is given off. After addition of all of the sulfur chloride solution the reaction mixture is re- The mixture is then the solvent A dark resin remains and is identified as an acetone polysulfide resin having the following formula:

Fifty-eight grams EXAMPLE 3 at from 8-1 perature of C. A sm out from the is 27.5 grams. The total yield is 112 grams, constituting a high yield of an isophorone polysulfide resin having the structural formula:

EXAMPLE 4 Seven hundred grams (1.6 moles) 2-liter, round-bottom Th hours. The bulk is distilled off at atmospheric is removed by vacuum disyield of one hour and the EXAMPLE Sixty-three and eight-tenths grams (1.1 moles) of aceml. of benzene are placed in a 3-neck,

.tone and 100 l-liter flask equipped with a reflux condenser and a dropping funnel. The solution is heated to boiling, and then a solution of 64 grams (2 gram-atoms) of sulfur and 135 grams (1 mole) of sulfur monochloride in 75 ml. of benzene is added dropwise during a period of about two hours. The mixture is refluxed for another hour and then is allowed to cool to room temperature. Solvent is removed by distillation under reduced pressure. The hot black resinous product is poured from the flask and is identified as an acetone polysulfide resin of the following formula:

One hundred thirty-eight and two-tenths grams (1 mole) of isophorone and 500 cc. of carbontetrachloride are placed in a l-liter, round-bottomed, 3neck flask equipped with reflux condenser and dropping funnel. One hundred and thirty-five grams of sulfur monochloride is added dropwise. The contents of the flask are refluxed for about six hours and the solvent is stripped off at atmospheric pressure. The remaining solvent and unreacted isophorone are distilled off at a reduced pressure of 24 mm. and a final temperature of 189 C. A substantial yield (119.5 grams) of isophorone polysulfide resin is obtained.

EXAMPLE 7 Ninety-eight and one-tenth grams (1 mole) of cyclohexanone is dissolved in 350 ml. of carbontetrachloride and introduced into a l-liter, round-bottomed flask equipped with reflux condenser and dropping funnel. The solution is heated to boiling and 135 grams (1 mole) of sulfur monochloride is added dropwise over a period of about two hours. The solution is then refluxed for an additional four hours with the HCl termed being absorbed in a water trap. The excess solvent is distilled off, the final portion being removed under vacuum at a final temperature of 150 C. and 50 mm. pressure. A 141.7 grams of dark brown, resinous material is obtained, constituting a high yield of a cyclohexanone polysulflde resin of the structural formula:

C-S- Z CH, CH; :1

EXAMPLE 8 One hundred ten and one-half grams (0.987 mole) of methyl cyclohexanone is dissolved in 300 ml. of carbontetrachloride and introduced into a round-bottomed flask equipped with reflux condenser and dropping funnel. The solution is heated at gentle reflux, and sulfur monochloride is added dropwise over a period of about solution is then refluxed for an additional five hours. The solvent was distilled away under vacuum with a final temperature of 144 C. A yield of 163.3 grams of dark resin is formed, constituting a high yield of a methyl cyelohexanone polysulfide resin having the structural formula:

5 2- -s-no o-s- --z 1120 CH: 10 011cm 11 In Table 1 below, Examples 9 and 10 are presented to illustrate the performance of the isophorone polysulflde resin prepared in accordance with this invention with that of elemental sulfur. All cures are in minutes at 280 F.

Table I Rubber Composition Exargnple Exalrgple Santoeure Stress-Strain Properties:

Modulus 400%- Aged Stress-Strain Pr Tensile Break- 2, 750 80 2, 550 120 2, 550 40 Elongation Break- 40 290 80 210 290 120' 220 290 1 Rubbery butadiene-styrene copolymer prepared by emulsion polymerization 4 1 Asphaltic flux product.

3 N-eyclohexy1-2-benzothiazole'sulienamide.

Table II Examples Rubber Composition SEE (LTP) 100.0 100.0 100.0 Carbon Black (HAF) 45.0 45. 0 45.0 Zinc Oxide 2.4 2. 4 2.4 Stearic Acid 2. 5 2. 5 2. 5 Isophorone Polysulfide 5. 0 4. 2 4. 2 Santoeure 1. 0 Stress-Strain Properties:

Modulus @400%- its 1: 300 3, 150 3, 225 2, 075

In Table III below, Examples 14-16 are presented to 7 resins of the invention with sulfur as a curing agent. 4. A resinous polysulfide polymer consisting essentially All cures are in minutes at 280 F. of repeating units of the following formula:

Table III OH Rubber Composition CH2 CH3 SBR LTP) Mb g B1 a ck HA h wherein m 1s an integer from one to three. Zinc Oxide 5. A resinous polysnlfide polymer consisting essentially 2 3 3? of repeating units of the following formula: su1rur 'II OH Cyclohexanone Polysulfide. I Methylcyclohexanone Polysulfid O I I 1 s E 'i" 1 t l5 OImS. TBSS- lalll roper 16S: Modulus 300% (s) (I: H (I: (s) 33: H2c on,

20 wherein m is an integer from one to three. 6. A resinous polysulfide polymer consisting essentially gg, of repeating units of the following formula:

0 385:: on Aged Stress-Strain Properties days 212 /O\ M i5 S s)m-oi-r o(s)..-

H3O CH2 r CH3 wherein m is an integer from "one to three.

7. A process for preparing a resinous polysulfide polys mer as defined by claim 1, which comprises reacting (l) an enolizable ketone which in the enol form has the struc- I tural formula: 1

3H HC1C=CzH I 1. A resinous polysulfide polymer consisting essenb radicals s lected f0 vth on Onsisfin of h dro en tia'lly of repeating units of the following formula: y e m e gr f g y g OH -(S)mC1d=l02(S)m saturation in said divalent hydrocarbon radical being a having the formula S X wherein w is an integer from wherein C and C are carbon atoms and wherein the inditwo to four and X is a halogen selected from the group cated free valences of such carbon atoms are satisfied by consisting of chlorine, bromine and iodine. substance selected from the group consisting of hydrogen, 8. The process of claim 7 in which the ketone is acetone. alkyl, acetyl and divalent aliphatic hydrocarbon radical 9. The process of claim 7 in which the ketone is acetyl llnking C and C and having three carbon atoms in a H acetone. straight chain between terminating valences, and any un- 05 10. The process of claim 7 in which the ketone is isosaturation in said divalent hydrocarbon radical being a phorone.

carbon-to-carbon double bond, and wherein m is an integer 11. The process of claim 7 in which the ketone is cyclofrom one to three. hexanone. (k

2. A resinous polysulfide polymer consisting essentially 12. The process of claim 7 in which the ketone is methyl of repeating units of the following formula: cyclohexanone. y 13. 'Ihe process of claim 7 in which the reaction is car- OH ried out in the presence of an inert organic solvent at reflux temperature.

14. A process of curing a sulfurvulcanizab le diene rubber polymer, which comprises admixing with the rnbwherein m is an integer from one to r her the resinous polysulfide polymer defined by claim 1,

3- A resinous pclvsulfide p y consisting essentially and heating the mixture to form a vulcanizate. of repeating units of the following formula: 15. The process of claim 14 in which the polysulfide polymer is defined by claim 2. OH 16. The process of claim 14 in which the polysulfide polymer is defined by claim 3.

The process of claim 14 in which the polysulfide COCH! polymer is defined by claim 4.

18. The process of claim 14 in which the polysulfide wherein m is an integer from one to three. 7 5 polymer is defined by claim 5.

19. The process of claim 14 in polymer is defined by claim 6.

which the polysulfide References Cited in the file of this patent UNITED STATES PATENTS Stem Baer

Mar. 13, 1917 Apr. 28, 1936 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,038,883 June 12, 1962 Lawrence E. Forman It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 20, for "halogen)." read halogen) same column 2, lines 28 to 32, the formula should appear as shown below instead of as in the patent:

Signed and sealed this 5th day of April 1966.

(SEAL) Attest:

EDWARD J. BRENNER ERNEST W. SWIDER Attesting Officer Commissioner of Patents 

1. A RESINOUS POLYSULFIDE POLYMER CONSISTING ESSENTIALLY OF REPEATING UNITS OF THE FOLLOWING FORMULA: 